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Scala reflection doesn't understand Java enumerations #6374

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scabug opened this issue Sep 14, 2012 · 4 comments
Closed

Scala reflection doesn't understand Java enumerations #6374

scabug opened this issue Sep 14, 2012 · 4 comments
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@scabug scabug commented Sep 14, 2012

enum SimpleEnumeration {
  FOO,
  BAR
}
import scala.reflect.runtime.universe._

object Test extends App {
  println(typeOf[SimpleEnumeration].declarations)
}
scala.reflect.internal.Symbols$CyclicReference: illegal cyclic reference involving type E
	at scala.reflect.internal.Symbols$Symbol$$anonfun$info$3.apply(Symbols.scala:1188)
	at scala.reflect.internal.Symbols$Symbol$$anonfun$info$3.apply(Symbols.scala:1186)
	at scala.Function0$class.apply$mcV$sp(Function0.scala:40)
	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
	at scala.reflect.internal.Symbols$Symbol.lock(Symbols.scala:468)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1186)
	at scala.reflect.internal.Types$$anonfun$40.apply(Types.scala:4316)
	at scala.reflect.internal.Types$$anonfun$40.apply(Types.scala:4315)
	at scala.reflect.internal.util.Collections$class.mapWithIndex(Collections.scala:122)
	at scala.reflect.internal.SymbolTable.mapWithIndex(SymbolTable.scala:12)
	at scala.reflect.internal.Types$class.typeParamsToExistentials(Types.scala:4315)
	at scala.reflect.internal.SymbolTable.typeParamsToExistentials(SymbolTable.scala:12)
	at scala.reflect.internal.Types$class.typeParamsToExistentials(Types.scala:4321)
	at scala.reflect.internal.SymbolTable.typeParamsToExistentials(SymbolTable.scala:12)
	at scala.reflect.internal.Types$$anon$11.apply(Types.scala:4352)
	at scala.reflect.runtime.JavaMirrors$JavaMirror.typeToScala(JavaMirrors.scala:1004)
	at scala.reflect.runtime.JavaMirrors$JavaMirror.typeToScala(JavaMirrors.scala:1007)
	at scala.reflect.runtime.JavaMirrors$JavaMirror$TypeParamCompleter$$anonfun$complete$1.apply(JavaMirrors.scala:567)
	at scala.reflect.runtime.JavaMirrors$JavaMirror$TypeParamCompleter$$anonfun$complete$1.apply(JavaMirrors.scala:567)
	at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
	at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
	at scala.collection.AbstractTraversable.map(Traversable.scala:105)
	at scala.reflect.runtime.JavaMirrors$JavaMirror$TypeParamCompleter.complete(JavaMirrors.scala:567)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1198)
	at scala.reflect.internal.Types$$anonfun$40.apply(Types.scala:4316)
	at scala.reflect.internal.Types$$anonfun$40.apply(Types.scala:4315)
	at scala.reflect.internal.util.Collections$class.mapWithIndex(Collections.scala:122)
	at scala.reflect.internal.SymbolTable.mapWithIndex(SymbolTable.scala:12)
	at scala.reflect.internal.Types$class.typeParamsToExistentials(Types.scala:4315)
	at scala.reflect.internal.SymbolTable.typeParamsToExistentials(SymbolTable.scala:12)
	at scala.reflect.internal.Types$class.typeParamsToExistentials(Types.scala:4321)
	at scala.reflect.internal.SymbolTable.typeParamsToExistentials(SymbolTable.scala:12)
	at scala.reflect.internal.Types$$anon$11.apply(Types.scala:4352)
	at scala.reflect.runtime.JavaMirrors$JavaMirror.typeToScala(JavaMirrors.scala:1004)
	at scala.reflect.runtime.JavaMirrors$JavaMirror.typeToScala(JavaMirrors.scala:1007)
	at scala.reflect.runtime.JavaMirrors$JavaMirror$FromJavaClassCompleter.completeRest(JavaMirrors.scala:653)
	at scala.reflect.runtime.JavaMirrors$JavaMirror$FromJavaClassCompleter.complete(JavaMirrors.scala:644)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1198)
	at scala.reflect.internal.Types$TypeRef.decls(Types.scala:2421)
	at scala.reflect.internal.Types$TypeApiImpl.declarations(Types.scala:298)
	at scala.reflect.internal.Types$TypeApiImpl.declarations(Types.scala:295)
	at Test$delayedInit$body.apply(Test.scala:4)
	at scala.Function0$class.apply$mcV$sp(Function0.scala:40)
	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
	at scala.App$$anonfun$main$1.apply(App.scala:61)
	at scala.App$$anonfun$main$1.apply(App.scala:61)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:32)
	at scala.collection.mutable.ListBuffer.foreach(ListBuffer.scala:45)
	at scala.App$class.main(App.scala:61)
	at Test$.main(Test.scala:3)
	at Test.main(Test.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:71)
	at scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
	at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:139)
	at scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:71)
	at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:139)
	at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:28)
	at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:45)
	at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:35)
	at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:45)
	at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:74)
	at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
	at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:105)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
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@scabug scabug commented Sep 14, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6374?orig=1
Reporter: @xeno-by
Affected Versions: 2.10.0
Other Milestones: 2.10.0

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@scabug scabug commented Sep 14, 2012

@xeno-by said (edited on Sep 17, 2012 12:05:00 PM UTC):
Here's the deal:

  1. SimpleEnumeration is being completed. Completion triggers typeToScala(superclazz), which is Enum
    =======
  2. typeToScala(Enum) recurs into typeToScala(Enum)
  3. typeToScala(Enum) = rawToExistential(typeRef(clazz.owner.thisType, clazz, List()))
  4. rawToExistential = existentialAbstraction(mapOver(typeParamsToExistentials(sym)), typeRef(apply(pre), sym, mapOver(typeParamsToExistentials(sym)) map (_.tpe)))
  5. typeParamsToExistentials = clazz.newExistential(newTypeName("?"+i), clazz.pos) setInfo tparam.info.bounds
  6. tparam.info = TypeParamCompleter.complete
  7. TypeParamCompleter.complete = sym setInfo TypeBounds.upper(glb(jtvar.getBounds.toList map typeToScala map objToAny))
  8. Since Enum is defined as Enum<E extends Enum>, jtvar.getBounds map typeToScala recurs back into Step 2, with the argument being not Enum, but Enum, which eventually leads to a cyclic reference

I can't immediately see how to evade the error. Could anyone chime in?

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@scabug scabug commented Sep 17, 2012

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@scabug scabug commented Sep 19, 2012

@scabug scabug closed this Sep 19, 2012
@scabug scabug added this to the 2.10.0-M7 milestone Apr 7, 2017
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